Synchronous Generator speed
Synchronous Generator speed
(OP)
We have a hydro powerhouse with 750KW 40Hz generators with 40 poles. We cannot increase the rotor speed to produce 60Hz. power. We have been told that the stator can be rewound to produce 60Hz. It seems like this would need 1.5 stator windings per rotor pole. There is only one winding per slot, so the slots are fairly shallow. It would be much easier to restack the stator core than to modify the rotor.
Has anyone tried this? Any thoughts? A vendor has said it might be possible, but has offered no details.
Has anyone tried this? Any thoughts? A vendor has said it might be possible, but has offered no details.





RE: Synchronous Generator speed
RE: Synchronous Generator speed
Changing the number and/or spacing of the stator poles without changing the number and/or spacing of the rotor poles may change the phase angle of some of the windings in a phase group and may not change the frequency.
Changing the number of rotor poles will change the frequency but with many coils generating at the wrong phase angle the terminal voltage at a given excitation current will be down.
Why can't you change the speed, The set is not that big and not running that fast.
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous Generator speed
RE: Synchronous Generator speed
old field guy
RE: Synchronous Generator speed
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous Generator speed
RE: Synchronous Generator speed
RE: Synchronous Generator speed
Maybe you could take a look wheel and mechnical design in order to study if you can redesign something that can help you increasing the mechanical speed like an alternative you could replace the actual generator by one with 54 poles and regulate.
I.M.O a comparisson between mechanical modification and generator replacement most done in order to have a technical- economic solution.
Regards
Carlos
RE: Synchronous Generator speed
It is an historic intallation, and has a web page. I will not reveal more, only the OP can do that.
The 6 40HZ generators are coupled to the 60Hz grid by two synchronous/synchronous frequency changer sets, or that was the arrangement. Perhaps the idea is to eliminate the frequency changers, or there is a fault in one of them??
A static frequency changer is possible of course and have been built for many different frequency combinations by amongst others, ABB, and Siemens. The 60/25 HZ
SFCs feeding Amtrak and SEPTA rail operations have been in service by now many years.
The Swedish Railways are fed by many SFCs working at 50/16.66 HZ.
It is an economic problem, likely, the cost of a HV SFC would far exceed the available funds for this relatively small plant.
rasevskii
RE: Synchronous Generator speed
RE: Synchronous Generator speed
RE: Synchronous Generator speed
If you wanted to produce 60hz, you would need to rewind both your stator and rotor for 60 poles
Regarding the stator:
[quote]There is only one winding per slot[quote]
Do you mean one coil per slot? i.e. single layer winding?
How many stator slots does this machine have?
If it is a multiple of 60, that makes the job easier. If it is not an exact multiple of 60, it would be a fractional slot winding. We can look at options for fractional slot winding when we know the number of slots.
Someone would have to look at physical installation /coil design so the end portions of the coil have adequate clearance
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(2B)+(2B)' ?
RE: Synchronous Generator speed
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(2B)+(2B)' ?
RE: Synchronous Generator speed
RE: Synchronous Generator speed
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RE: Synchronous Generator speed
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RE: Synchronous Generator speed
Remove half the rotor poles & install three layers of stator winding?
By the way, at 60Hz. we want only 4160V, not 12KV.
RE: Synchronous Generator speed
Due to the increasedd voltage rating at the same current, the KVA rating must increase by 50% to 150%.
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous Generator speed
2/3 slots per pole per phase.
If we attempt to develop a fractional slot winding, some pole phase groups have 1 slot allocated and some have zero allocated. Already we suspect that will result in a lot of harmonics, but we need to figure out the coil layout to balance the fundamental among phases first:
A reference here:
thread237-261447: Question for experienced rewinders
You have q = 120/(3*60) = 2/3
A =0, b = 2, c = 3
With c=3, you cannot perfectly balance the fundamental in this configuration. You would have to leave some slots empty to do that. I’m sure there are quite a few more challenges even in designing the stator and balancing fundamental of stator among phases may be among the smaller ones. But in my view it is first step to find the winding configuration to balance the fundamental and second step to evaluate harmonic performance of that winding configuration. I am doubting this existing stator core can be rewound for 60 poles without substantial derating and lots of harmonics and vibrations. If your shop thinks they can do it, then I would ask them to tell me how they are going to lay out the coils (with that info we can evaluate the harmonics).
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(2B)+(2B)' ?
RE: Synchronous Generator speed
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RE: Synchronous Generator speed
How about cutting the number of poles in half on both the rotor and stator. Then slow the turbine down to get 60 Hz. Any solution will involve compromise and I suspect a reduction in the KVA rating.
Consider any one coil. The number of rotor poles passing in one revolution will induce a 40 Hz EMF. Changing the number of poles on the stator may result in some interesting harmonics but it won't change the frequency.
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous Generator speed
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(2B)+(2B)' ?
RE: Synchronous Generator speed
Cutting poles in half would give 20 poles.
To get 60hz with a 20 pole machine would require you to operate at speed of 360rpm.
That’s going in the wrong direction.
The machine is currently operating at 120rpm and can’t exceed 140rpm
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(2B)+(2B)' ?
RE: Synchronous Generator speed
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronous Generator speed